Repeater system



2 Sheets-Sheet 1 ma sem INVENToR 61 ATTORNEY Se1:t.'23, 1930. G. cRlssoN ,REPEATER SYSTEI Filed June '7, 1928 Sept. 23, 1930. AQ CRISSQN 1,776,311

REPEATER SYSTEM Filed June '7, 192B 2 Sheets-Sheet 2 ,Phantom 'l'callt Ref/water INV ENTOR ATTORNEY 15 compositing apparatus to Patented Sept. 23, 1930 UNITED STATES PATENT OFFICE GEORGE CRISSON, F EAST ORANGE, NEW JERSEY, ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK REPEATER SYSTEM Application nled June 7, 1928. Serial No. 283,639.

This invention relates to repeaters for use in signaling systems, and particularly to a form orrepeater circuit in which two .2l-type repeater circuits are so associated with the line circuit that there is a continuous metallic .path from each conductor of the line on one side of the repeater to a corresponding conductor of the line on the other slde of the repeater. Direct currents or alternating currents of a frequency too low to be amplified by the repeater may pass through these metallic paths without interfering with the action 'of the repeater with respect to waves of-higher frequency and without requiring the use of permit the passage of such direct or low frequency alternating currents.

One property of this repeater circuit is that three of them may readily be connected with 2o the line conductors of a phantom -group so as to am lif the'waves traversing either of the si e circuits or the phantom Without requiring the use of phantom repeating coils; Another useful property is that it does not transmit amplified waves back toward the transmitter and therefore, does not produce echoes other than those due to irregularities in the line. 4 v

This invention resides primarily in a repeater circuit comprising two 2l-type re;-

peater circuits associated with the line circuitI by means of a hybrid coil or other suitable network which rovides a substantially con ju-gate relation etween the two 21-type cir-l cuits and between the parts of the line circuit lying on opposite sides of the repeater.

The way in which this invention may be carried out is vdescribed completely in the' following paragraphs and the accompanying drawings of whlch Figure 1 is a simplified drawing of a 21-type repeater circuit; Fig. 2 shows a 21-type repeater circuit in greater detail; Fig. 3 is a dia' ram of a repeater circuit embodying this lnvention; and Fig. 4 shows three repeater circuits embodying this cludes a 'hybrid coil, or three-winding transinvention which are combined to form av former H, two of whose vwindings 1, 1 and 2, 2 are connected in series between thetwo parts LW and LE of a transmission circuit such as, for example, a telephone line. The

input terminals of an amplifier A of any suitable type are connected across the line circuity at the junctions between the windings 1, l and 2, 2. The output terminals of the amplifier A are connected to thepthird winding 3 of the hybrid coil.A A reversing switch S is ineluded in either the output 0r input circuit of the amplifier. Assume now that a signal wave enters the repeater from the line LW. If the input and output impedances ofthe amplifier lare chosen to obtain the most efficient transrival of the incoming Wave at the repeater causes a current to How at some instant from one line wire into one-half winding of the hybrid coil, for example l, and out of. the half winding-1 to the other wire as indicated by the heavy solid arrows. The emission of the amplified wave in both' directions causes a' current to fiow inseries through-both line windings and both parts of the line as indicated,'for example, by the dotted arrows.

1 Assuming first, for simplicity, that there is no phase shift in the amplifier, there is one position of the switch S in which the input and output currents flow in the same direction in the wires of the line Lw. Let this arrangement be designated as the direct connection.' If now, the switch S is thrown to the opposite position, the direction of the output current is reversed so that this current flows in the opposite direction to the input current. Let this arrangement be designated as the reversed connection.

Now assume that the switch S is thrown to ive the direct connection to the line LW as lmicated in Fig. 1, but assume further that a.

wave is arriving over the line LE and that at a given instant the input current is flowing into the half winding 2 from the line LE and out of the half winding 2 to the line LE. This current will flow in the same direction in the input circuit of the amplifier as the input current previously assumed as coming from the line LW. The output currents will now flow in the direction indicated by the dotted arrows as before, but they are now flowing in the opposite direction to the input currents. From this it is evident that a 21-type circuit that is direct connected with respect to the line LW will be reversed with respect to LE and by throwing the switch S to the other position, the 21-type -circuit becomes direct with respect to LE and reversed with respect to LW.

Fig. 2 shows in greater detail a 21-type repeater circuit including a vacuum tube amplifier with the connections so arranged that the circuit is direct with respect to the line LE and-reversed with respect to the line LW. Fig. 3 showsone form of my invention. It comprises a hybrid coil H1, connected between the two parts of a telephone line eX- tending to the two stations marked East and West stations, respectively. To the third. winding 3 ofthe hybrid coil H, is connected a 21-type repeater circuitX which is 'direct connected with respect to the hybrid coil H1,

A network N1 and transformer T3 are connected to the opposite terminals of the 21- type circuit to balance the hybrid coil H1 land the two parts of the line. If this balance is good enough, the 2l-type circuit cannot sing. Between the terminals'l-l of winding 3 and terminals 13-14 of transformer 'L is connected the hybrid coil H2 comprising the windings 1 -4', 5 5 and 6. The input circuit of the amplifier A.; is connected with the junction points. of the windings 1li-4' and 5-5. the connection including the transformer T5; and the output circuit of the amplifier is connected with the winding 6.

A second 21-type repeater circuit Y is con# nected to the bridge points of the hybrid coil Hl through the condensers C.l and C3. The condenser (3 resistance R1, and the network N2 are connected to the opposite terminals` of t-he 21-type circuit Y to balance the condensers C2 and C3, the resistance of the line windings l, l and 2, 2 'of the hybrid coi-l H2 and the lines Lw and LE. The 21-type circuit Y is reversed with respect to the hybrid coil H1. Y Between the terminals -13-14 of the condensers Ctand C3 and the terminals 15-16 associated with the network N2 the condenser C1 and resistance R1 is connected the hybrid coil H3 compris-` ing the windings 7-7, 8 8`v and 9. The

input circuit of the amplifier A2 is connected vwith the junction points of the windings 7-7 and`8--8, the connection including the transformer T5; and the output rcircuit of the amplifier is connected with the winding 9.

Now let a wave arrive at the hybrid coil H1 over theline LW. At a given instant let the current flow from the line LW into the half winding 1 of the hybrid coiland from the half winding 1 to the line LW as indicated by the light straight arrows. This current liows in the two 2l-typecircuits which in turn cause amplified currents to flow in their own circuits and in the lines. Due to its direct connection the 21-type repeater X causes an amplified current to flow at the terminals 15, 16 in the same direction as the input current. This amplified current is repeated by the hybrid coil H1 and fiows into the two parts of the line as indicated by the solid heavy arrows.

Since the 2l-type circuit-Y in reversed connection with the line, its amplified cur. rent flows at the ter1ninals'13, 14 in the 0pposite direction to the input current. In the line this current takes the directions indicated by the wavy arrows. It will be observed that the output currents How in the saine direction in the line LE reinforcing each other, while in the line LW extending toward the source of-the waves, the output currents flow in opposite directions and tend to annul each other.

In this way the .complete repeater of this invention transmits an amplified wave to-l ward the listener, but by properly adjusting the gains of the two 21-type repeaters, the waves that tend to travel toward the speaker arecompletely cancelled out sothat no echoes are produced.

Similarly, if a wave reaches the repeater over the line LE, causing a current that flows into the half winding 2 of the hybrid coil I-Land out of the half winding 2. the output current'from the .2l-type circuit X will be reversed in direction while that from the S21-type circuit-Y will flow in the same direction as before.- The output waves will now lon reinforce each otherin the line Lw and cancel out in the line LE. A repeater built in accordance with this invention will therefore amplify waves reaching it from either direction over the line and send the amplified wave toward the receiving end of the line wit-hout returning echoes toward the source.

In the foregoing discussion it was assumed. for simplicity, that there was no phase shift in the process of amplification so the amplied waves were strictly in phase with or in opposition to the incoming wave. It will be observed, however. that if equal phase shifts do occur in the two 21-type circuits, the f output currents will still add up in phase or oppose each other as before, hence phase shifts do no harm provided they are equal in the two 21-type circuits'. It was also assumed that the v21-type circuits X andY were directly and reversely connected, respecof the transformers T2 and T2 This affords means for connecting with ther tively, with respect to the lines but it will readily be seen that if Y is directly and X reversely connected with the lines, the invenl tion willstill operate in the manner described, since both output waves will be reversed in direction and the reinforcement of the desired Wave and cancellation of the echo will occur as before.

The phaseshift introduced by the fact that the inductance of the hybrid coil H1 is not infinite is in the same direction as that introduced by series condensers C2 and C3 and varies in the same way with frequency; hence by choosing suitable capacities for these condensers with respect to the inductance of the hybrid coil H1 and the impedance of the lines, these phase shifts may be equalized. The condensersC2 and C3 also serve to prevent the passage ofdirect or low frequency alternating currents into t-he 21type circuit Y; consequently there is an uninterrupted and unshunted path for such currents through the line windings of the hybrid coil H1 from the line LW to LE. This avoids the necessity for using compositing apparatus to provide a path for such currents around the repeater.

Fig. 4 shows how three repeater circuits working in accordance with this invention may be assembled in a phantom group so that the waves traversing each side and the phantom circuit may be amplified without interference with each other and without using phantom repeating coils. As in the arrangement of Fig. 3, the metallic continuity of the several line conductors of this phantom group is preserved' through the repeater circuit.

In this iigure, LW and LE represent sections of a line, which are connected with terminals of the hybrid coil H1. A twin 21stype repeater, designated side circuit repeater No. 1, is connected with the said line sections through the hybrid coil H1. Similarly, LW

and LE are sections of another line connected with terminals of the hybrid coil H1 through which another twin 21-type repeater, designated side circuit repeater N o. 2,'is connected with the said line sections.

The said side circuit repeaters diier from that shown in Fig. 3 only in the manner in which the amplifying elements are associated with the hybrid coils H3 and H3. In Fi 3, a direct connection is shown, Whereas in `ig. 4 the said elements are connected by means respectively.

lines .La-LE and LM-LE one` of the 2l-type repeaters of the phantom circuit repeater. This is done by connecting the midpoints of the primary windings of the transformers T2 and T2 with the terminals of the hybrid coil H.,Y associated with the bridged 21-type repeater that constitutes one of the units of he twin 21-type repeater of the phantom circuit.I The other 21-type repeater ofthe phantom group is connected with the conductors of the line circuits by means of the transformer T6 comprising a lurality of windings upon the same core. ne winding (shown in two sections) is connected with the terminals .of the hybrid coil H5 and the others are individual to and connected with thc conductors of the sections of the said lines. The phantom circuit repeater simulates the side circuit repeaters and operates in substantially the same manner. It will therefore be apparent that by means of threc Ql-type repeaters, arrangedin the manner shown in Fig. 4, it is possible to amplify the waves traversing both side circuits and'also the phantom circuit without introducing interference and without rendering the circuit discontinuous for direct currents, which would result if phantom coils were employed.

lVhile this invention has been disclosed as embodied in particular forms, it is ca able of embodiment in other and different orms without departing from the spirit and scope of the appended claims.

lV hat is claimed is:

1. A repeater comprising a hybrid coil inserted between the two parts of a transmission circuit extending in opposite directions, a directly connected .Q1-type circuit and a reversely connected 21-type circuit, both of which are associated withthe line through the hybrid coil.

2. In a repeating system, the combination with a transmission circuit of a directly connected 21-type circuit in series relation therewith, a reversely-connected 2l-type circuit in parallel relation with the transmission circuit, and means for effecting the said series andl parallel relations.

3. In' a repeating system, the combination `with a transmission circuit of a directly connected 21-type circuit in series relation therewith and a reversely connected 21-type circuit in parallelv relation with the transmission circuit.

4. In a repeating system, the combination with a transmission circuit of a 21-type circuit, in series relation therewith, a second 21 type circuit in parallel relation therewith, one of said 21-type circuits being-directly and the other reversely connected with respectA to the transmission circuit, and means for eiecting'the said series and the said parallel connections.

5. In combination, a. transmission circuit, a hybrid coil interposed between the parts thereof extending in opposite directions, a first 21-type circuit connected in series relation with the transmission circuit through the hybrid coil, a second Ql-type circuit connected in parallelwith the transmission circuit at the bridge terminals of the hybrid coils, one of said 2ltype -circuits being directly and the other reversely connected'with respect to the transmission circuit, condensers' interposed in series between the said sec-v ond 21type circuit and the said hybrid coil, a network associated with each 21-type circuit adapted to balance the transmission circuit, the hybrid coil andthe co-ndensers, and means for adjusting the gains of the two 2l-typel circuits while keeping the gains equal.

6. The method of amplifying signaling waves traversing a transmission circuit, which consists in impressing the said waves simultaneously upon two Ql-type repeater circuits, impressing the amplified waves from one 21- type circuit upon the sections of the transmission line on both sides of the repeater in series, and impressing the amplified waves from the other 21-type repeater upon the said sections .in parallel.

. 7. The method of amplifying signaling waves traversing a transmission circuit, which consists in impressing the said waves simultaneously upon two S21-type repeater circuits, impressing the amplified waves from one l21-type circuit upon the sections of the transmission line on both sides of the repeater in series, and impressing the amplified waves A from the other 21-type repeater upon the said sections in parallel, controlling the degree of amplification of the said 21-type repeaters so that the amplified waves from both repeaters are of the same magnitude, and directing them so that' they reinforce each other in that part of the transmission circuit extending toward the receiver and annul each other in that part of the transmission circuit that extends toward the transmitter.

l8. A- phantom group of repeaters comprisl ing three repeaters each of which consists of a hybrid coil and t-wo 21-type circuits, the windings of each hybrid coil associated with a side circuit being inductive tov that side circuit and non-inductive to the phantom and the windings of the phantom hybrid coil being inductive to the phantom and non-inductive to both side circuits` two 21-type circuits associated with each hybrid coil, one being in series relation and the other in parallel relation with the corresponding side or phantom circuit, one of said 21-type circuits being di- Y rectly and theother reversely connected with respect to the lhybrid coils, networks associated with each`21-type circuit adapted to balance the side or phantom circuit and the hybrid coil to which the 21-type circuit is connected, condensers in each conductor which extend from either conductor of each side circuit to the other conductor of the ,said side circuit, and means for adjusting the gain of each 21-type circuit While keeping equal the 'gains of the two 21-type circuits associated with each hybrid coil.

9. The method of amplifying signaling waves traversing a transmission circuit,

which consists in dividing the waves into two parts, amplifymg the said parts and reimpressing them upon the said circuit, and controlling the degreeI of amplification and the direction of application of the said parts to the said transmission circuit so that they reinforce each other in that part of the circuit extending toward the receiver and annul each other in that portion of the line extending toward the transmitter. p

10. A'repeater for connection with a line circuit comprising a three-Winding transformer and two 21-type repeater circuits, the said transformer having two windings connected with said line and the third winding connected withV one of the said 21-type circuits, the other Ql-type circuit being bridged across the midpoints of the line windings of the said transformer.

In testimony whereof,

June, 1928.

GEORGE CRISSON. 

